How to use a reference material

General

To ensure an effective use of reference materials, it is necessary to obey all instructions concerning intended use, stability (shelf life and storage conditions), sample preparation, minimum sample intake, etc., given by the RM-producer on the certificate or in accompanying documentation.

A specific RM can only be used for a single purpose in a given measurement (e.g. calibration or validation/verification). If one CRM is used for calibration, another CRM must be used for validation.

If an RM is used for, for example, calibration or quality control, the user has to choose a material as similar as possible to the test sample. This comprises the matrix composition as well as the content level of the analyte of interest.

Calibration using RMs

Reference materials – pure substances as well as matrix RMs – are often used for calibration purposes. If matrix RMs are used for calibration, it has to be ensured that the matrix of the RM is behaving sufficiently similarly in the calibration process to the test sample to cope with potential matrix influences for the measurement method used. Calibration can be done using one or several different RMs. The uncertainties associated with the property values of the RMs have to be considered when the uncertainty contribution due to calibration is evaluated.

Validation - Verification of a measurement result [2]

To verify a measurement result, the difference (Δ_m) between the measured (c_m) and certified value (c_CRM) of the CRM has to be compared with the combined uncertainty (μ_Δ) of the CRM (μ_CRM) and the measurement (μ_m).

If < 2 u _^ then there is no significant difference between the measurement result and the certified value.

Establishment of metrological traceability [3]

Use of a CRM is a convenient way to demonstrate metrological traceability. If the property value of the CRM is traceable to, for example, the SI, then the measurement involving it allows a statement concerning the metrological traceability of the results to SI units. However, metrological traceability can only be established when the uncertainty of the property values of the CRM is duly taken into account and if the nature of the analytical sample is sufficiently matched by the matrix and analyte level of the CRM.

For additional information see:

[1] ISO-Guide 33 (2000) Use of certified reference materials

[2] ERM application note 1 Comparison of a measurement result with the certified value

notes/application_note_1/application_note_1_english_en.pdf)

[3] ERM application note 3 Using reference materials to establish traceability

(http://www.erm-crm.org/html/ERM_products/application_notes/application_note
_3/ERM_application_note_3_-_Mar08__4_.pdf)